Firefox can falsely report that an update is available when you already have the latest version of Firefox installed. If you are experiencing this problem, one of the following solutions may resolve the issue:
You can download the setup file for the latest version of Firefox from http://www.mozilla.com and install it on top of your current Firefox installation. For more information, see Installing Firefox. You will not lose any settings, bookmarks, passwords, add-ons, or any other information if you reinstall Firefox.
Delete update configuration files
Click the menu button
and then click ExitQuit
Delete the following files:
The updates folder and its contents
These files may be found in one or both of the following locations:
The folder where you installed Firefox (e.g., on Windows, C:\Program Files\Mozilla Firefox).
The folder where local application data and settings are stored for Firefox. This location depends on your operating system. For example, in Windows XP, the location may be: C:\Documents and Settings\<username>\Local Settings\Application Data\Mozilla\Firefox\Mozilla Firefox, where <username> corresponds to the username that you used to log in to your computer.
After the files are deleted, restart Firefox. The configuration files will be rebuilt in the proper locations.